Sono and electrochemical synthesis and characterization of copper core–silver shell nanoparticles

Cu–Ag core–shell nanopowders have been prepared by ultrasound-assisted electrochemistry followed by a displacement reaction. The composition of the particles has been determined by X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX). The XRD patterns versus time displacement show that higher are the silver peaks intensities, weaker are the copper ones. That exhibits the progressive recovering of copper by silver. EDX results and quartz crystal microbalance results indicate that various reaction mechanisms are implied in this process. Transmission electron microscopy (TEM) points out variable nanometric diameter grain and some small agglomerates. Elemental mapping obtained by electron energy-loss spectroscopy (EELS) underlines the core–shell structure.     

Structure, phase composition, and optical properties of silicon nanopowders

The nanopowders obtained by sputtering of silicon with a high-power electron beam in nitrogen and argon atmospheres have been investigated by transmission electron microscopy, Raman spectroscopy, photoluminescence spectroscopy, ultrasoft X-ray emission spectroscopy, and X-ray absorption near-edge structure spectroscopy. The sizes of particles and their phase composition have been determined. A mechanism is proposed, which explains the visible photoluminescence of nanopowders.     

Methods of electron microdiffraction and X-ray analysis in structure study of nanodisperse partially stabilized ZrO2 powders

Analytical electron microscopy (AEM) has been used to study both structure and morphology of partially yttria-stabilized zirconia dioxide nanopowders (YSZ) obtained by wet-chemical methods (glycine and azeotropic distillation) and ceramics produced from them. Both morphological and structural inhomogeneity of nanopowders obtained by glycine (glc) method has been estimated. Besides the tetragonal ZrO₂ phase (results of X-ray analyses) the cubic phase of ZrO₂ with different degree of crystallinity has been estimated by Electron Microdiffraction (EMD) methods. In powders obtained by azeotropic distillation (dest) method besides the amorphous phase (identified in X-ray investigations) the high disperse cubic zirconia phase has been identified using high local EMD method. It has been detected the yttrium influence on the degree of crystallinity in nanopowders obtained by azeotropic distillation method without yttria (dest-0YSZ) and with 5 wt % Y₂O₃ (dest-5YSZ). It has been determined the difference in ceramic morphology produced from these powders. Ceramics mode of nanopowders containing yttria (glc-5YSZ and dest-5YSZ) have a homogeneous surface which consists of different size globules (0.1–0.6 μm) and contains some little pores (～370 nm). Ceramics mode of nanopowders without yttria have inhomogeneous surface with numerous cracks. Separate parts of the latter ceramics consist of globules, their sizes are of 0.2–0.5 μm.     

Effect of iron doping on the structural and magnetic properties of ZnO nanoparticles prepared by pulsed electron beam evaporation

Nanocrystalline ZnO, ZnO-Zn, and ZnO-Zn-Fe powders with a specific surface area up to 45 m²/g and a low Fe concentration (no more than 0.619 wt %) have been prepared using pulsed electron beam evaporation. The crystal structure, morphology, and size of the nanoparticles have been determined using X-ray powder diffraction, transmission electron microscopy, and scanning electron microscopy. It has been found that the magnetization of the ZnO-Zn and ZnO-Zn-Fe nanopowders increases after annealing in an oxidizing atmosphere. An elemental mapping with energy-dispersive X-ray analysis has revealed the absence of Fe clusters in the ZnO-Zn-Fe sample. A thermal analysis has demonstrated that dopants of Fe in ZnO increase the temperature of complete oxidation of Zn nanoparticles to 600°C, which creates favorable conditions for an increase in the density of structural defects upon oxidation of Zn to ZnO. The absence of clusters and secondary magnetic Fe phases in pure and doped ZnO-based nanopowders indicates the intrinsic nature of ferromagnetism at room temperature in nanopowders prepared by pulsed electron beam evaporation.     

Preparation of conventional thermoelectric nanopowders by pulsed laser fracture in water: application to the fabrication of a pn hetero-junction

The technique of laser fracture in a liquid medium has been applied to the synthesis of n-type (Bi_0.95Sb_0.05)₂ (Te_0.95Se_0.05)₃ and p-type (Bi_0.2Sb_0.8)₂Te₃ semiconducting nanopowders which are the best conventional materials currently used for thermoelectric applications at ambient temperature. The nanopowders have been prepared with a high yield in an especially built-up cell. Laser fracture in water of micronsized powders has been applied, using a nanosecond Nd:YAG laser working at 532 nm. The obtained powders have been characterized by scanning and transmission electron microscopy and by X-ray diffraction. The mean diameter is about 10 nm and the phase of the initial powders is kept. To test the potentiality of these nanosized materials, we have shown the feasibility to produce a pn hetero-junction.     

Preparation and reactivity of aluminum nanopowders coated by hydroxyl-terminated polybutadiene (HTPB)

HTPB-coated aluminum (Al) nanopowders were prepared by laser-induction complex heating. The characterization of the nanopowders was revealed using transmission electronic microscopy (TEM), high-resolution transmission electronic microscopy (HRTEM), X-ray diffraction analysis (XRD) and Fourier transform infrared (FTIR) spectrometry. Results showed that HTPB-coated Al nanopowders have a core-shell structure with size ranging from 30 to 100 nm and organic HTPB exists in HTPB-coated Al nanopowders. Differential scanning calorimeter (DSC) and thermal gravimeter (TG) analysis of the HTPB-coated Al nanopowders and Al₂O₃-passivated Al nanopowders stored for 2 years in ambient environment indicated that the reactivity and stability of HTPB-coated Al nanopowders outperform Al₂O₃-passivated Al nanopowders. These findings demonstrate that HTPB is a suitable surface coating material for Al nanopowders.     

Investigation of magnetic properties of Al substituted nickel ferrite nanopowders, synthesized by the sol-gel method

NiFe_2−xAl_xO₄ nanopowders, where x is from 0 to 1.5 with a step of 0.5, have been synthesized by the sol-gel method and the effect of non-magnetic aluminum content on their structural and magnetic properties were investigated. The X-ray diffraction (XRD) patterns revealed that the synthesized nanopowders are single phase with a spinel structure. Mean crystallite sizes of the samples were calculated by Scherrer's formula and were in the range 20-31 nm. The morphology of the nanopowders was investigated by TEM and the mean particle sizes of the samples were in the range 55-80 nm. Magnetic hysteresis loops were recorded at room temperature in a maximum applied field of 3000 Oe. The results show that by increasing the aluminum content, the magnetizations of the nanopowders are decreased. This reduction is caused by non-magnetic Al³⁺ ions, which by their substitutions the super exchange interactions between different sites will be reduced. It is also seen that the magnetizations of the nanopowders are lower than those related to their bulk counterparts. This reduction was found to be as a consequence of surface spin disorder. M-T curves of the samples were obtained using a Faraday balance and by which the Curie temperatures of the powders were determined. The results that are obtained show that the Curie temperatures of the nanopowders are higher than those of their bulk counterparts.     

电爆炸丝法制备纳米Al2O3粉末

 设计了电爆炸金属丝产生纳米金属氧化物粉末的实验装置，金属丝电爆炸腔采用圆筒结构，纳米粉末经过微孔滤膜过滤收集。成功制备了纳米Al₂O₃粉末，其平均粒度达到64.9 nm。对电爆炸金属丝产生纳米Al₂O₃粉末的物理条件进行了研究。结果表明实验条件对粉末粒度有重要影响：随气压的增加粉末平均粒度变大；随金属丝直径增大粉末平均粒度变大；粉末的平均粒度与电容器的初始储能也有一定的关系。     

Improvement of photocatalytic behavior of chemical-vapor-synthesized TiO2 nanopowders by post-heat treatment

Anatase-type TiO₂ nanopowders less than 10 nm in average diameter were synthesized by a chemical vapor synthesis method. The TiO₂ nanopowders showed very poor photocatalytic properties, in spite of their large surface area. With subsequent heat treatment of the TiO₂ powders, their photocatalytic properties determined by measuring the degradation of 2-propanol were improved at temperatures up to 600 °C and then diminished along with formation of a rutile phase. This improvement in the photocatalytic properties of TiO₂ nanopowders was attributed to both a morphology change and a change in the electronic surface characteristics of TiO₂ particles during heat treatment.     

Electric explosion nickel nanopowders

The structure and the morphology of the nickel nanopowders synthesized by an electric explosion of a metallic wire are comprehensively studied. The results of scanning and transmission electron microscopies show that the nickel nanoclusters have a spherical shape with an average diameter of 50 nm. An analysis of X-ray diffraction patterns demonstrates that the lattice parameter of the electric explosion nanopowder particles is larger than the standard parameter. The results of computer experiments agree well with the conclusions drawn from X-ray diffraction data. However, the causes of the lattice distortion in the nickel nanoclusters are still debatable.     

氩气中铝丝电爆炸沉积能量对制备铝纳米粉体特性的影响

研制了基于脉冲电容器放电回路的亚微秒金属丝电爆炸纳米粉体制备实验平台,包括电爆炸过程电流和电压测量系统。利用透射电子显微镜(TEM)观察纳米粉体的形态与结构,并通过电镜统计观察法分析TEM图像得到纳米粉体的粒度大小及其分布。在氩气中电爆炸铝丝制备铝纳米粉体,通过改变电容器充电电压,即初始储能,实验研究沉积能量对铝纳米粉体特性的影响规律。结果表明:铝纳米粉体颗粒形态与结构主要由氩气气压的高低决定,与沉积能量基本无关。增大丝爆过程的沉积能量可显著缩小铝纳米粉体粒度分布范围,减小颗粒平均粒径,并有效地抑制纳米粉体中亚微米颗粒的形成。随着沉积能量E与氩气气压p比值(Ep-1)增大,铝纳米粉体颗粒平均粒径、最大粒径和粒径大于100 nm颗粒所占比例均呈指数函数单调减小。     

NBT-Eu纳米粉体的水热合成及其发光性能研究

采用水热合成法、在不同条件下制备Na0.5Bi0.49Eu0.01Ti O3(NBT-Eu)纳米粉体。通过X射线粉末衍射(XRD)、紫外-可见光谱、透射电子显微镜、荧光光谱对样品进行表征。结果表明,在200℃、碱浓度12 mol·L-1、反应时间24 h、添加剂OP-10用量为0.6 m L时,可以得到纯三方钙钛矿结构的NBT-Eu粉体,该粉体以直径为15~200 nm的纳米棒形式存在。NBT-Eu粉体在458 nm激发下,产生689 nm的荧光,该荧光由Eu3+的5D0→7F4能级跃迁产生。     

Effect of small particle sizes on the measured density of nanocrystalline powders of nonstoichiometric tantalum carbide TaC<Subscript> <Emphasis Type="Italic">y</Emphasis> </Subscript>

Nanocrystalline powders of the nonstoichiometric tantalum carbide TaC_y (0.81 ≤ y ≤ 0.96) with an average particle size in the range from 45 to 20 nm have been prepared using high-energy ball milling of coarse-grained powders. The density of the initial coarse-grained and prepared nanocrystalline powders of TaC_y has been measured by helium pycnometry. The sizes of particles in tantalum carbide powders have been estimated using the X-ray diffraction analysis and the Brunauer–Emmett–Teller (BET) method. The density of TaC_y nanopowders measured by helium pycnometry is underestimated as compared to the true density due to the adsorption of helium by the highly developed surface of the nanocrystalline powders. It has been shown that the difference between the true and measured densities is proportional to the specific surface area or is inversely proportional to the average particle size of the nanopowders. The large difference between the true and measured pycnometric densities indicates a superhydrophobicity of the tantalum carbide nanopowders.     

Structure comparison of PMN–PT and PMN–PZT nanocrystals prepared by gel-combustion method at optimized temperatures

We have synthesized and were performed a comparison of structures and optical properties between relaxor ferroelectric PMN–PT and PMN–PZT nanopowders. A gel-combustion method has been used to synthesize PMN–PT and PMN–PZT nanocrystalline with the perovskite structure. The precursors employed in the gel-combustion process were lead nitrate, magnesium acetate, niobium ammonium oxalate and zirconium nitrate. The nanopowders were characterized using the X-ray diffraction (XRD) and transmission electron microscopy (TEM) observation. Fourier transform infrared (FTIR) spectroscopy was employed to monitor the transformation of precursor solutions during the thermal reactions leading to the formation of perovskite phase.     

Synthesis and electrochemical properties of Ni doped titanate nanotubes for lithium ion storage

Ni doped titanate nanotubes were synthesized by hydrothermal method using Ni doped rutile TiO₂ nanopowders as a starting material. The electrochemical properties were investigated by cyclic voltammmetric methods. The microstructure and morphology of the synthesized powders were characterized by XRD (X-ray diffraction), and HRTEM (high resolution transmission electron microscopy). Ni doped nanotubes were composed of H₂Ti₂O₅·H₂O with outer and inner diameter of ∼10 nm and 6 nm and showed a initial discharge capacity of 305 mAh/g with poor cycling performance. However, after firing, the Ni doped nanotubes revealed better cycling performance due to lower reaction with hydrate and smaller diameter of the tubes.     

Eu3+和Tb3+掺杂硅酸钇纳米粉体的合成与表征

采用溶胶-凝胶法合成了Y₂SiO₅∶Eu和Y₂SiO₅∶Tb纳米粉体,使用X射线衍射仪、扫描电镜等对粉体的结构、形貌和发光性能进行了分析,研究了Eu³⁺和Tb³⁺不同浓度掺杂硅酸钇纳米粉体的发光性能。在紫外光激发下,所获得的Y₂SiO₅∶Eu纳米粉体的主发射峰均位于612 nm,对应于Eu³⁺的⁵D₀→⁷F₂跃迁;Y₂SiO₅∶Tb纳米粉体的主发射峰均位于540 nm,对应于Tb³⁺的⁵D₄→⁷F₅跃迁。     

Structural and cathodoluminiscent properties of Zr0.95Ce0.05O2 nanopowders prepared by sol-gel and template methods

Nanopowders of Zr_0.95Ce_0.05O₂ composition have been prepared by a standard Pechini-type sol-gel process and by means of a colloidal crystal template approach. In the latter method, inverse opal Zr_0.95Ce_0.05O₂ powders were fabricated employing poly(methyl methacrylate) (PMMA) colloidal crystals as a template. The effects of the two different synthesis routes on the structure and microstructural characteristics of the prepared nanopowders were evaluated by X-ray diffraction and scanning electron microscopy. For both preparation routes, the X-ray diffraction analysis has shown that a tetragonal fluorite structure is formed with a crystallite size of ∼35-40 nm. The scanning electron microscopy measurements indicate that the powder obtained by the sol-gel Pechini-type process is comprised of nanoparticles that are arranged in agglomerates with shape and size relatively uniform whereas the inverse opal Zr_0.95Ce_0.05O₂ nanopowders exhibit the formation of macropores with a mean size of ∼100 nm. The cathodoluminescence spectra of the prepared Zr_0.95Ce_0.05O₂ nanomaterials have been measured in the 300-800 nm wavelength range. The powder prepared by sol-gel method yields a broad emission band centered at 482 nm whereas the emission from the inverse opal preparation is considerably less intense.     

纳米粉体CeO_2∶Eu~(3+)的溶胶-凝胶绿色合成及其发光性质

采用溶胶-凝胶法,以硝酸铈为原料,加入适量淀粉为分散剂,并通过氨水来调节溶液p H值,合成稀土Eu~(3+)掺杂的CeO_2红色纳米粉体。通过X射线衍射仪、场发射扫描电子显微镜、荧光分光光度计等手段研究不同煅烧温度对粉体结构、形貌、发光及显色性能的影响。结果表明,所得样品为立方晶系的萤石结构,空间群为Fm3m,颗粒呈近似球形,粒径范围在10~60 nm之间。随着煅烧温度的升高,CeO2晶粒尺寸逐渐增大,荧光粉的红色发光也逐渐增强。经800℃烧结后,近紫外(370 nm)和蓝光区(468 nm)的光都能对粉体有效地激发,这有利于其在固态照明中的应用。在溶胶-凝胶制备过程中,采用淀粉作分散剂,具有工艺简单、绿色环保的优点,有利于纳米氧化铈粉体的大规模制备。     

LaPO_4∶Ce,Tb纳米荧光粉末的合成及其在指纹无损显现中的应用

采用溶剂热法在水和乙二醇的混合溶剂中合成出了高质量的LaPO_4∶Ce,Tb纳米荧光粉末。然后通过透射电子显微镜(TEM)、粉末X射线衍射(XRD)、荧光光谱(FS)等表征手段分别对稀土纳米荧光粉末的微观形貌、晶体类型、荧光性能进行了表征,合成纳米荧光粉末的形貌为单分散的纳米棒,平均长度为700nm、平均直径为20nm,其晶体结构为单斜LaPO_4晶型,并且在254nm紫外光照射下能够产生较强的绿色荧光。最后将合成的纳米荧光粉末应用于光滑客体表面汗潜指纹的无损显现中,并详细考察了指纹显现的对比度、灵敏度、选择性、背景干扰等指标。实验结果表明,使用LaPO_4∶Ce,Tb纳米荧光粉末显现的指纹在254nm紫外光的激发下能够产生明亮的绿色荧光,指纹乳突纹线部位连贯清晰、细微特征反映明显,指纹与客体之间的对比反差强烈、客体产生的背景干扰较小,因此该显现方法具有较高的对比度、灵敏度和选择性。本显现方法具有操作方法简单、显现效果优良、适用范围广泛等优点。本研究的重要创新之处在于,经LaPO_4∶Ce,Tb纳米荧光粉末显现后的指纹还可以进行后续的DNA提取及检测,这是传统的指纹显现粉末所不能及的。本研究为指纹物证和生物物证这两大物证的同时利用提供了有益参考。     

Study of energy transfer from capping agents to intrinsic vacancies/defects in passivated ZnS nanoparticles

The study of energy transfer mechanism from different capping agents to intrinsic luminescent vacancy centres of zinc sulphide (ZnS) has been reported in the present work. Nanoparticles of capped and uncapped ZnS are prepared by co-precipitation reaction. These nanoparticles are sterically stabilized using organic polymers—poly vinyl pyrrolidone, 2-mercaptoethanol and thioglycerol. Monodispersed nanoparticles were observed under TEM for both capped and uncapped ZnS nanopowders. However, for uncapped ZnS nanopowders, tendency for formation of nanorod like structure exists. Size of ZnS crystallites was calculated from X-ray diffraction pattern. The primary crystallite size estimated from X-ray diffraction pattern is 1.95–2.20 nm for capped nanostructures and 2.2 nm for uncapped nanostructures. FTIR spectra were conducted to confirm capping. Zeta potential measurements have been done to check the stability of dispersed nanoparticles. Band gap measurement was done by UV–visible spectrophotometer. Excitation and emission spectra are also performed in order to compare optical properties in various samples. Increase in emission intensity and band gap has been observed by adding different capping agents in comparison to uncapped ZnS nanoparticles. The results show that in capped ZnS nanoparticles the mechanism of energy transfer from capping layer to photoluminescent vacancy centres is more pronounced.